Amplifier for short electric waves



March 17, 1931. c SOUTHWORTH 1,796,486

AMPLIFIER FOR SHORT ELECTRIC WAVES Filed May 1, 1926 11v VEN TOR G. C. 'out/zwmrt/z Patented Mar. 17, 1931 STATE r NT rricn -SFJY, ASSIGNGB TO AMERICAN TELE- PHONE AND TELEGRAPH CGMEPELNY, A CORPORATION OF NEW YORK AMIPLIFIEB FOR SHOE,

Application f led May 1, 1926.

This invention relates to means for amving short electric waves, and more parariy to means suitable for amplifying uating voltages an d currents of frequenhigher than those now generally used adio communication.

It is desirable that the frequency range available for communication purposes be materially extended. This is so especially becauseof the approaching need for a greater number of radio speech channels in View of the threatened congestion in the communication spectrum.

'VVith the technique universally employed in the commercialfield at the present time, engineers are confronted, in their efforts to produce very high frequencies for communication purposesthat is, to produce ultraradio frequencies for use in radio communication, with the requirementof inductances and capacities so small as to be impracticable. At frequencies as low as three megacycles per second (3 mo), corresponding to a wave length of one hundred meters (100 111.), such all.

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7 small coils and condensers are required that stray inductances imposed by connecting wires and extraneous capacities between pieces of apparatus often present Clll'TlQllltlES which are considerable. When a frequency of approximately 30 mc., corresponding to a wave length of approximately 10 m., is reached, the coils and the condensers required are miniatures of the apparatus used in commercial radio practice, their inductances and capacities being but little greater than those of the necessary connecting wires.

It is the object of applicants invention to provide means suitable to commercial use for producing alternating voltages and currents of ultra-radio frequencies and of such amplitude as to be useful in the practice of radio communication.

Applicant accomplishes his purpose by employing a three-electrode vacuum tube amplifier and applying methods new in the amplification of alternating voltages and currents to'the solution of the problems of impressing the high frequency alternating volton the grid and of relaying the amplified Waves. r

the magnetic to the electric state.

resonant conditmn is obtained by the ad- WAVES Serial No. 106,132.

In the vacuum tube amplifiers now in general use for amplifying alternating voltages and currents of radio frequencies, that is, frequencies lower than perhaps 30 mo, the grid and the filament of the tube are connected in a circuit, usually known as the input circuit, having localized inductance furnished by a coil and localized capacity furnished by a condenser, the grid and the filament being connected to the terminals of the condenser. Electromagnetic energy is applied to the circuit, and a resonant condition of the circuit is set up, in which condition the'energy is periodically transformed from This justment of the localized capacity or the localized inductance or both. At the time when the energy is wholly electric, or substantially so, the condenser is charged, and a relatively high voltage is impressed between the grid and the filament, this voltage controlling the electron stream from the filament to the plate. The-natural period of oscillation of the circuit depends upon the time required for the ener y to change from the magnetic to the electric state in the coil and condenser. 1

instead of adopting the methods discussed above, applicant makes use of a wave circuit, defined below, in which electromagnetic energy in the form of a wave travels in the space bet-ween two conductors and is reflected from the ends of a rectangle. The term wave circuit, as used by applicant, desighates an extended circuit in which conductors are used to guide electric waves, or, in other words, a circuit the physical dimensions of which are appreciable in comparison with the length of the waves. Such a circuit may also be considered as a circuit'having distributed inductance and capacity, as distinguished from localized inductance and capacity. In the wave circuit, the natural period of oscillation depends on the length of the conductors as compared with the wave length, or, in other words, as compared with the frequency of the alternations. Various distinctions between the radio frequency amplifier and applicants ultra-radio frequency amplifier will be more fully pointed out after a description has been given of one desirable embodiment of this invention.

The invention will he clearly understood from the following description of a desirable embodiment thereof. This description is to he read with reference to the accompanying drawing); Figure l of the drawing shows diagrannnatically applicants circuit so arranged that high trequency alternating voi are amplified. and a considerahle pogtion it the energy radiated. Fifi. 2 shows (liagrainmatically an arrangement of he circuit for amplifying the currents and communicating the output of the amplifier to the succeeding ci1'cuitot a. radio receiring s tem, for instance. 3 shows an arrangement similar to that oi 2. but involving a dilierent method 0t coupling; between the anr plilier and he succeeding circuit.

In each 0? the three circuits shown.

filament 5, plate 6 and grid The input or the end.

The alternating; eiectromotire force is communicated to the input circuit. in the a; rangements shown in the drawing, from the circuit 1 1:, which includes a cleetromot ve force. It is to he no limitation is placed on the see vention by the specific showii e' here since it l will he clear to taos up in the input circuit 1y any one a 1 r. 1 of well known methods. the choice o e most suitahle he' determined h particular use to he i of the amplifier.

' hen a relatively s alternating: eleeire force is applitd to the input e 1c we will. flow along 9. or, ricwe l somewhat re wares to he amnhfie;

with a relocit fap he re wave will QtQSwQJnCQ is produced by adjustment of the length. of the conductors 8 and 9 reiatire to the frequency of the appli l 4: t i a tromotire iorce. Any wave circi satisfactory which comprises con suitah conducter m id consignc \l 17k arranged that it may he readily adjust as to n and lilflTiSl-T-DS. The conductors shown in the drawing are cylindrical and of substantial diameter and are in two telese ping sections, whereby length adjustment is readily made. The required length oi the ware circuit relative to the frequency oi? the applied eleetromotive force will he generally discussed hereinafter.

V-fhen the energy is applied or reflected at the left end ot the input circuit (with reil ei ence to the drawing) it is mainly magnetic. At an intermediate point between this end of the circuit and the vacuum tube end. it is hoth magnetic and electric. When the energy r vaches the tnhe end oi? the (.llCllid. it is mainly electric. and it will he readily understood by those skilled in. the art that a relatirelylarg e voltage w' ll he impressed hetween e clecron cam between the fila- 1 ate c ti hanging the plate cur- :n'

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output or p ate circuit of the tuhe 4: is 'ned, lilze the input circuit, to guide the c wares, set up in this case hy the gee; in the voltage between the plate and ent. due to the grid voltage changev nut circuit comprises the guiding 10 and 11 terminating at the let t end in the plate and the filament. respectively. and formed in accordance with the dispo ition to h made of the output energy the amplifier. If it is desired to radiate energy directly into the ether. the guiding conductors 10 and 11 ac widely separated anl may be either open, shown in Fig. l. or closed. If, however, it is desired to communicate the enere y output to another circuit. tor instance the circuit including a. succeeding amplifier tube or a detector tuhe in 1 recs all? set, the guiding conductors are atively close together, and are, for

iectly. as shown in Fig. 2. or by the indi reet inductive method of Fig; 3. The condnceors 10 and 11 are preferably constructed and {K justed as are the input circuit conduc- In order to produce the condition. of resonance in a simple wave circuit is it approximately accurate to say that in the case of conductors closed or open t both ends, the length of the conductors mu. he equal to one-half the length of? the rmyes and in the case of conductors closed one end and open at the other. the lene'th of the conductors must be equal to 0ne-tourth the length of the waves. If. however. a wave circuit closedv at hoth ends is terminated in a capacity. the length of the condutors which is reonired for resonance will he. in most cases, slightly greater. This condition exists in the circuits shown in 2 and 3 of the drawing, since the wave circuits are term nated in either the gridfilament capacity or the plate-filament ea pacity of the tube. Again, if a Wave circuit is closed at one end and terminated. in a ca pacity, the length of the conductors will be slightly less than in the simple case, in most instances. If the tube capacity terminating the wave circuit is so large that the requirements for resonance, as stated above, would lead to a rectangle too short to be practicable for coupling, the rectangle should be lengthened by one-half the Wave length or any multiple thereof. In other words, the guiding conductors will now be so adjusted, in the case of conductors closed at both ends, as to make the length of the wave circuit approximately one-half the wave length or equal to the Wave length, or to one and one-half times the wave length, or to twice the wave length, etc. Likewise, in the case of conductors open at only one end, th length of the conductors will be adjusted to make the wave circuit length approximately onefourth of the wave length or equal to three-fourths of the wave length. or to one and one-fourth times the wave length, or to one and three-fourths times the wave length, etc. membered that the tube capacity renders nec essary circuit lengths somewhat different from those indicated above.

It will help to clarify the description of applicants amplifier to note the following di 'tinctions between the radio frequency amplifier and the ultraradio frequency amplifier embodying the invention- In the case of the former, the impressed grid voltages are derived from energy oscillating from the magnetic state to the electric state in a coil and a condenser. The natural period of oscillation is determined by the time required for the energy to change from the magnetic to the electric state in these elements, which, in turn, depends on their inductance and capacity. The oscillations take place in a space very small in comparison with the length of the waves to be produced. In applicants amplifier, the energy is in the form of an electro-magnetic wave guided along the conductors. In the input circuit, when the energy reaches the grid, it is electric and provides the necessary voltage for operating the tube. The natural period of oscillation is determined by the time required for a wave to travel the length of the rectangle and be reflected back. The oscillations take place in a space appreciable when compared with the Wave length.

W'hile applicants invention has been described in a specific embodiment for the purpose of illustration, it is to be understood that it is capable of embodiment in other and different forms without a departure from the It is to be re-' cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, and an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance.

2. An amplifier of electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance, means for impressing electric waves on said input circuit, and means for communicating electric energy from said output circuit.

3. A system for amplifying electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance,

and an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance, said input circuit and said output circuit being adjustable as to form and dimensions.

4. An amplifier of electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode; an input circuit including said cathode and said control ling electrode, and an output circuit including said cathode and said anode, said circuits having only distributed capacity and distributed inductance and being adjustable as to form and dimensions; means for impressing electric waves on said input circuit; and means for communicating electric energy from said output circuit. 1

5. In a system for amplifying electric waves, including a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having, only distributed capacity and distributed inductance.

6. In a system for amplifying electric waves, including a vacuum tube having an anode, a cathode, and a controlling electrode, an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance.

7.111 a system for amplifying electric waves, including a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, said circuit being adjustable as to form and dimensions.

8. In a system for amplifying electric waves, including a vacuum tube having an anode, a cathode, and a controlling electrode, an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance, said cir cuit being adjustable as to form and dimensions.

9. In a system for amplifying electric waves, a vacuum tube having an anode, a cathode, and a. controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, and an energy supplying circuit as sociated with said input circuit, said energy supplying circuit being associated with said vacuum tube only through said input circuit.

10. A system for amplifying electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance, and an energy supplying circuit associated with said input circuit, said energy supplying circuit being associated with said vacuum tube only through said input circuit.

11. An amplifier of electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode, an output circuit ineluding said cathode and said anode, means for impressing electric waves on said input circuit, and means for communicating electric energy from said output circuit, said input and said output circuits each having only distributed capacity and distributed inductance in addition to any inductance or capacity which may be involved in the coupling between said circuits and the impressing means and the communicating means respectively.

12. An amplifier of electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode; an input circuit including said cathode and said controlling electrode; an output circuit including said cathode and said anode; means for impressing electric waves on said input circuit; and means for communicating electric energy from said output circuit; said input and said output circuits being adjustable as to form and dimensions and having each only distributed capacity and distributed inductance in addition to any inductance or capacity which may be involved in the coupling between said circuits and the im pressing means and the communicating means respectively.

13. In a system for transmitting electric waves, comprising a vacuum tube having an anode, a cathode, and a controlling electrode,

an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance, and an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance.

14. in a system for transmitting electric waves including a vacuum tube having an anode, a cathode, and a controlling electrode, an input circuit including said cathode and said controlling electrode and having only distributed capacity and distributed inductance.

15. In a system for transmitting electric waves, including a vacuum tube having an anode, a cathode, and a controlling electrode, an output circuit including said cathode and said anode and having only distributed capacity and distributed inductance.

In testimony whereof, I have signed my name to this specification this 29th day of April, 1926.

GEORGE G. SOUTHVVORTH. 

